Python-Django/C2/Django-Shell-and-Django-Database-Query/English

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Django/C2/Django_Shell_and_Django_Database_Query/English

Title of script: Django Shell and Django Database Query

Keywords: Video tutorial, Django Shell, Django Database Query


Visual cue Narration
Slide: Django Shell and Django Database Query Hello and welcome to the spoken tutorial on “Django Shell and Django Database Query”.
Slide: Learning Objectives In this tutorial, we will learn to:
  • Use the Django shell and
  • Create a Django Query
Slide: System Requirements To practice this tutorial, I am using
  • Ubuntu Linux 16.04 OS
  • Python 3.5
  • Python 3.4-venv or higher
  • gedit Text Editor

However, you can use any other text editor of your choice.

Slide: Prerequisites To follow this tutorial, you need to know
  • How to create models in Django
  • If not, then please go through the prerequisite tutorials in this series.
Slide: What is the Django Shell ?
  • The Django shell is a Python shell configured for our Django project.
  • We can execute our project code in this shell.
  • We can manipulate our app models in this shell.
Open a Terminal window

Press CTRl+ALT+T simultaneously

Let us open the terminal by pressing Ctrl, Alt and T keys simultaneously on your keyboard.
[Terminal]

cd my-django [Enter]

Now using cd command, we will go to the folder my hyphen django which we had created earlier.
[Terminal]

Type source myapp_env/bin/activate [Enter]

Activate the virtual environment myapp underscore env
[Terminal]

cd mysite and Press Enter

Now let us go to the folder mysite.
Here onwards, please remember to press the Enter key after typing each command.
[Terminal]

Type python manage.py shell [Enter]

Let us now type the command-

python manage dot py <space> shell

[Terminal]

Highlight (point to the shell)

(InteractiveConsole)

>>>

We are now in the Interactive console.
Slide: Interactive console
  • The Interactive console provides a perfect complement to the Python environment
  • It allows interactive editing, running and debugging of our Python project
Switch to Terminal Switch back to terminal.
[Terminal]Type:

from blog.models import Blog [Enter]

from django.utils import timezone [Enter]

blog = Blog(name='My Second Blog', created_on=timezone.now()) [Enter]

blog.save() [Enter]

Let us run a Django query to add a new Blog.

Type the commands one by one as shown here.

[Terminal]

Highlight

from blog.models import Blog

To add a new Blog, we need to import Blog from our models.
[Terminal]

Highlight

blog = Blog(name='My Second Blog', created_on=timezone.now())

Here we have created a Blog instance.
[Terminal]

Highlight

blog = Blog(name='My Second Blog', created_on=timezone.now())

Also, we have added values to its fields - name and creation date.
[Terminal]

Highlight

created_on=timezone.now()

created_on attribute is not needed while creating a new blog object.


This is because we have already defined a default value for created_on attribute in models.


For learning purpose, we have shown how to assign a value to created_on attribute..

[Terminal]

Highlight

from django.utils import timezone

To get the creation date, we import timezone from django dot utils module.
[Terminal]

Highlight

blog.save()

Then, save the object that we have created.

So, Django writes this information to the database table Blog.

[Terminal] Type:

blog.id [Enter]

Let's now access the model field values through Python attributes.

To do so, type blog dot id

[Terminal]

In Output, Highlight 2

Here, the output shows two.

It is the id of the Blog object that we have created now.

[Terminal]

Type blog.name [Enter]

To display the name of the Blog object, type blog dot name
[Terminal]

In Output, Highlight 'My Second Blog'

Our Blog object name 'My Second Blog' is being displayed.
[Terminal]

Type blog.created_on [Enter]

To see the date time values of our Blog object, type

blog dot created underscore on

[Terminal]

In Output, Highlight datetime.datetime(....)

Here, it shows the date and time when the Blog was created.
[Terminal]

Type:

blog.name = 'This is a blog from shell' [Enter]

Let us now change the name of our Blog object.


To do so, type blog dot name equal to within single quotes the new name for the blog.


I have typed- “This is a blog from shell”.

[Terminal] Highlight

blog.name = 'This is a Blog from shell'

This will change the name in the output as This is a Blog from shell.
[Terminal] Type blog.save() [Enter] Save the blog.
[Terminal] Type blog.name [Enter] Then recall the blog dot name command and execute it.
[Terminal] In Output, Highlight

'This is a Blog from shell'

We can see the name as 'This is a Blog from shell'


So far, we have created and made changes on a Blog object via shell.

[Terminal]


Type:

Blog.objects.all() [Enter]

To get all Blog objects using Query, type


Blog dot objects dot all opening and closing parentheses

[Terminal] In Output, Highlight

<QuerySet [<Blog: Blog object (1)>, <Blog: Blog object (2)>]>

In the output, we can see the Queryset with a list of Blog objects.


Blog object in the output is not a good representation for the object.

[Terminal]


Press Ctrl + D keys

Let us fix this in the models.py file.


Quit from the shell by pressing Ctrl and D keys together.

[Terminal]


Type gedit blog/models.py & [Enter]

Then open the models.py file in any text editor.
[blog/models.py]


from django.db import models

# Create your models here.

class Blog(models.Model):

name = models.CharField(max_length=120)

created_on = models.DateTimeField(auto_now_add=True)

def __str__(self):

return self.name

class Article(models.Model):

blog = models.ForeignKey(Blog, on_delete=models.CASCADE)

created_on = models.DateTimeField(auto_now_add=True)

title = models.CharField(max_length=120)

body = models.TextField()

draft = models.BooleanField(default=False)

def __str__(self):

return self.title

We are now in the models.py file.


Add a string method below the class Blog and Article as shown here.


For ease of practice, this code is provided in the Code Files link of this tutorial.


Please download, unzip and use it.

[models.py]

Highlight

def __str__(self):

We define a String method inside the class to get string representation of the object.
[models.py]

Highlight

return self.name

Here, the String method returns the name of our Blog model.
[models.py]

Highlight

return self.title

Similarly, for the Article model, let’s return the title.
[models.py]

Highlight the complete code

We have added the string method.

So now when we retrieve a Blog object,

we will see its name.

Lets understand this better.

Press Ctrl+S Save the file.
Switch to Terminal Then switch to the terminal.
[Terminal] Type:

python manage.py shell [Enter]

And activate the Shell.
[Terminal]In Shell, Type:

from blog.models import Blog [Enter]

Import the blog models.
[Terminal]In Shell, Type:

Blog.objects.all() [Enter]

And run the Django Query as we did before.
[Terminal] In Output, Highlight

<QuerySet[...<Blog: This is a blog from shell!...']>

It returns all the instances of the Blog model along with its name.
[Terminal]



Press Ctrl + D keys

Now, let's add a custom method to the Blog model in models.py file.


Quit from the shell.

Switch to models.py file Switch to the models.py file.
[models.py]

from django.db import models

from django.utils import timezone

# Create your models here.

class Blog(models.Model):

name = models.CharField(max_length=120)

created_on = models.DateTimeField(auto_now_add=True)

def __str__(self):

return self.name

def was_created_recently(self):

return self.created_on >= timezone.now() - timezone.timedelta(days=1)

Now, modify the class Blog as shown here.


Also import the timezone module from django.utils

[models.py] Highlight timezone.now() timezone.now() returns a date time that represents the current time.
[models.py] Highlight timezone.timedelta timedelta expresses the duration difference between
  • two dates,
  • two time inputs or
  • two date-time stamps.
[models.py] Highlight

from django.utils import timezone

To store timezone information, we import package timezone from django dot utils module.
[models.py]

Highlight

def was_created_recently(self): return self.created_on >= timezone.now() - timezone.timedelta(days=1)

The "method was created recently” checks whether the Blog is created more recent than a day.


This is done by subtracting 1 day from the current time.


Then comparing, if the saved time is greater than that.

[models.py] Highlight the complete code So we have added the method to Blog.
Press Ctrl+S Save the file.
Switch to Terminal Switch to the terminal.
[Terminal] Type:

python manage.py shell [Enter]

And activate the shell.
[Terminal] In Shell, Type:

from blog.models import Blog [Enter]

Import the blog models.
blog = Blog.objects.get(name=”This is a Blog from shell!”) [Enter]


blog1 = Blog.objects.get(name=”My First Blog”) [Enter]

The variable ‘blog’ has been lost as we quit from the shell to modify our model.


Let us retrieve a blog object by using get() method as shown here.

[Terminal] Type:

blog.was_created_recently() [Enter]

Now, to check whether the Blog has been created recently,

type-


blog dot was underscore created underscore recently opening and closing parentheses

[Terminal]In Output, Highlight

True

Here, the result says TRUE.

This is because blog was created recently in the shell few minutes back.

[Terminal] Type:

blog1.was_created_recently() [Enter]

Run the command again for variable ‘blog one’.
[Terminal]In Output, Highlight

False

Here, the result says FALSE as first blog was not recently created.

Note: The above results may vary as per your creation dates.

[Terminal] Type:

blog2 = Blog.objects.filter(id=2) [Enter]

Let us do filtering with Django Queries

Type the command as shown.

[Terminal]

Highlight

blog2 = Blog.objects.filter(id=2)

Here, the Queryset is evaluated.


Then, we fetch the result of a Blog object for which the id is two.


Since the id is unique, we get only one result.

[Terminal] Type: blog2 [Enter] Let us access the object, by typing blog two.
[Terminal] In Output, Highlight

<QuerySet [<Blog: This is a Blog from shell!>]>

The output returns the new Queryset containing the object that matches the given parameter.

Here, Queryset gives the respective Blog instances for the id two.

[Terminal] Type: blog2[0].id [Enter] To get the id, type the command as shown.
[Terminal] In Output, Highlight 2 The output shows the id for the given Blog object.
[Terminal] Type: blog2[0] [Enter] Now, type blog two two within square brackets zero
[Terminal] In Output, Highlight

<Blog: This is a Blog from shell!>

In the output, we get the blog object.

If we want a single blog object and it exists.

[Terminal]

blog2 = Blog.objects.get(id=2)

In this case we should use get query.

To do so, type the command as shown.

[Terminal] Type: blog2 [Enter] Let us access the object, by typing blog two.
[Terminal] In Output, Highlight

<Blog: This is a Blog from shell>

It will return the Blog object referred by its id.
Let us now try to get the Blog objects based on the year of creation.

First import the timezone from django.utils

[Terminal] Type:

current_year = timezone.now().year [Enter]

Blog.objects.filter(created_on__year=current_year) [Enter]

Then type the code as shown here one by one.
[Terminal]

Highlight

Blog.objects.filter(created_on__year=current_year)

Double underscores are used for Field Lookups.

It returns a new Queryset containing the objects that match the given lookup parameters.

[Terminal] In Output, Highlight

<QuerySet [<Blog: … >, <Blog: ... >]>

This query will return all the Blog instances created in this year.
[Terminal]Type:

blogs = Blog.objects.all() [Enter]

Now, let us understand the Queryset return method.

To do so, type code as shown.

[Terminal]Type:

blogs.count() [Enter]

To count the Blog objects, type blogs dot count opening and closing parentheses
[Terminal] In Output, Highlight 2 The output gives the count of Blog objects.
[Terminal] Type Blogs.

(press Tab)

To know the available method for the Queryset return, type Blogs dot

Press the Tab key to see the number of available methods.

[Terminal]

(pointing to the shell prompt)

Here, we can see a list of methods to return the Queryset.

Note: These methods can be directly used with objects as follows:

Blog dot objects dot <method>

[Terminal]Type:

blog = Blog.objects.get(id=1) [Enter]

For example, to get a Blog Object, use the get() lookup parameter.

Type the command as shown here.

[Terminal] Type:

blog.article_set.all() [Enter]

To get the related objects to the blog i.e. Articles, we use blog dot article_set dot all
[Terminal] In Output, Highlight

<QuerySet [<Article: My Article>]>

Every Article is related to a Blog because of the Foreign Key relationship.
[Terminal] Type:

from blog.models import Article

Article = Article.objects.get(id=1) [Enter]

blog1 = Article.blog [Enter]

blog1.id [Enter]

Also, we can access the information of the Blog object through it's related Article object.


To do that, type the following command one by one as shown here.

[Terminal] In Output, Highlight 1 We get one as the output.

This is our Blog object's id.

[Terminal] Type:

blog2.delete() [Enter]

Now, using delete() method, the object gets deleted.

Type blog two dot delete opening and closing parentheses

[Terminal]

(Pointing to the shell prompt)

In Output, Highlight (1, {‘blog.Blog’: 1, ‘blog.Article’: 0})

In output, it returns the number of objects deleted.


And a dictionary with the number of deletions per object type.

[Terminal]

Type Blog.objects.get(id=2) [Enter]

Then we use get with id two by typing

Blog dot objects dot get within parentheses id equal to two

[Terminal]

(pointing the Error)

The output throws Exception as “Blog does not exist”.

This indicates that the Blog object we had created, has been deleted.

[Terminal]

(pointing the Error)

get query will always return a single object.


If there are more than one match or no match, then it will throw an error.

In that case, it's advisable to use filter.

[Terminal] Type:

Blog.objects.filter(id=2) [Enter]

Let us do filtering with id two by typing

Blog dot objects dot filter within parentheses id equal to two

In Output, Highlight <QuerySet []> The result is a Null Queryset.
So, we have learnt to create a Django Database Query using Django Shell.
Terminal] Press Ctrl+C keys

Type deactivate [Enter]

Exit from the shell.

Deactivate the virtual environment.

Switch to slide With this, we come to the end of this tutorial

Let us summarize.

Slide: Summary In this tutorial, we have learnt to
  • Use the Django shell and
  • Create a Django Query
Slide: Assignment As an assignment,
  • Create and access an Article object within Blog model using Django Query in Shell
Slide: About Spoken Tutorial project The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.

Slide: Spoken Tutorial workshops The Spoken Tutorial Project team conducts workshops and gives certificates.


For more details, please write to us.

Slide: Forum for specific questions: Please post your timed queries in this Forum.
Slide: FOSSEE to answer questions Please post your general or technical questions in this Forum.
Slide: Acknowledgement Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.


More information on this mission is available at this link.

Slide: Thanks Slide This script has been contributed by Thiagarajar College of Engineering and the FOSSEE Project, IIT Bombay.

The video has been recorded by Praveen from Spoken Tutorial Project, IIT Bombay.

Thanks for watching.

Contributors and Content Editors

Nancyvarkey, Pravin1389

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